The present invention relates to a push-button switch of simple structure and highly reliable operation and a push-button switch device using such a push-button switch.
Conventionally, in a push-button switch device such as a pendant push-button switch device, used for a hoist crane, for example, a push-button switch is provided, in addition to a contact for an operating circuit for operating equipment (Contact A), with a contact for a verification circuit for verifying the state of return of the push-button switch, for example, the open state of the contact for the operating circuit at the time of closing of power, (Contact B). Note, for example, Japanese Utility Model Publication No. 52-53374.
This push-button switch is constructed in such a way that, by being incorporated in a push-button switch device provided with a sequence circuit consisting of operating circuit 7 and verification circuit 8, as shown in FIG. 12, for example, the main electromagnetic contactor MCO is not turned ON even if the power closing switch PB1 is operated in the state where the push button of the push-button switch does not release for reasons of failure of the push-button switch. It is believed that most incidents due to biting of dust (hereinafter referred to simply as "failure of the push-button switch" in the state where at least one of the contacts for the operating circuit is closed. In this case, the contact for the verification circuit corresponding to the closed contact for the operating contact is in the open state.
It is believed that most incidents of the push button of a push-button switch not releasing is believed to be produced more often because of a breaking of the spring for returning of the push button, or locking of the push button as a result of biting of dust in the sliding part of the push button, when the push button of a push-button switch for operating equipment is released from the pressed state, rather than when the push-button switch is out of operation.
However, in the case of a push-button switch device incorporating the conventional push-button switch, because the contact for the operating circuit remains closed when the pressed push button of a push-button switch cannot return when the push-button switch is being operated for operating equipment, (in other words, in the state where the main electromagnetic contactor MCO is turned ON), it is necessary for the operator to operate the switch PB2 for shutting off the power source to stop the equipment. However, in a pendant push-button switch device used for a hoist crane, for example, the operator cannot fully follow the movement of the pendant push-button switch device because the pendant push-button switch device moves together with the hoist crane and therefore cannot manage to operate the switch PB2 for shutting off the power source, thus presenting a risk of reckless use of the hoist crane without any means for preventing such eventuality. For that reason, a push-button switch device incorporating conventional push-button switches could not always fully achieve the purposes of raising the reliability of push-button switch operation and improving the safety of operation of the equipment as originally intended to.
Moreover, in the case of a push-button switch device provided with a conventional sequence circuit consisting of an operating circuit 7 and verification circuit 8, as shown in FIG. 12, there was a problem that the presence or not of any failure of the push-button switch for operating the equipment cannot be judged unless either the main electromagnetic contactor MCO is not turned ON even if the switch PBI for closing power is operated or the equipment does not stop even when the push button of the push-button switch for operating the equipment is released from the pressed state.